Carrier aggregation, in which a wireless communications device simultaneously transmits and receives radio frequency (RF) signals over multiple RF frequency bands, has become increasingly popular in order to increase data throughput. Supporting carrier aggregation in a wireless communications device presents several challenges in the design and manufacture of the device. One such challenge is illustrated in FIG. 1, which shows a wireless communications network 10 including a wireless communications device 12, a first base station 14A, and a second base station 14B. While the wireless communications device 12 is located much closer to the first base station 14A than the second base station 14B, the device may communicate with both the first base station 14A and the second base station 14B simultaneously using separate RF frequency bands. For example, the wireless communications device 12 may communicate with the first base station 14A using a Long Term Evolution (LTE) mid-band operating band and communicate with the second base station 14B using an LTE high-band operating band. Simultaneously communicating with the first base station 14A and the second base station 14B over different RF frequency bands increases the amount of data that may be transmitted from the wireless communications device 12 in a given amount of time, but it may also complicate the design of feedback circuitry used in a transmitter of the device to control the transmit power of the RF signals provided therefrom, as discussed with respect to FIG. 2 below.
FIG. 2 shows a conventional RF front end circuitry 16 with closed loop transmit power control. The conventional RF front end circuitry 16 includes an antenna 18, a diplexer 20, a first duplexer 22A, a second duplexer 22B, a first power amplifier 24A, a second power amplifier 24B, first RF coupler circuitry 26A, second RF coupler circuitry 26B, and feedback receiver circuitry 28. The diplexer 20 includes a common node 30A coupled to the antenna 18, a first input/output node 30B coupled to the first duplexer 22A via a first RF transmission line 32A, and a second input/output node 30C coupled to the second duplexer 22B via a second RF transmission line 32B. The diplexer 20 is configured to pass RF transmit signals and RF receive signals within a first RF frequency band between the first input/output node 30B and the common node 30A while attenuating other signals in this path. Further, the diplexer 20 is configured to pass RF transmit signals and RF receive signals within a second RF frequency band between the second input/output node 30C and the common node 30A while attenuating other signals in this path. Accordingly, the diplexer 20 allows for simultaneous transmission and reception of RF signals within the first RF frequency band and the second RF frequency band.
The first duplexer 22A includes a common node 34A, a transmit signal node 34B, and a receive signal node 34C. The common node 34A is coupled to the first input/output node 30B of the diplexer 20. The transmit signal node 34B is coupled to an output of the first power amplifier 24A. While not shown, the receive signal node 34C is often coupled to a low noise amplifier (LNA) for amplifying receive signals provided thereto for further processing. The first duplexer 22A is configured to pass first RF transmit signals TX1 from the first power amplifier 24A between the transmit signal node 34B and the common node 34A while attenuating other signals in this path. Further, the first duplexer 22A is configured to pass first RF receive signals RX1 from the common node 34A to the receive signal node 34C while attenuating other signals in this path. Accordingly, the first duplexer 22A allows for simultaneous transmission and reception of signals within the first RF frequency band.
The second duplexer 22B includes a common node 36A, a transmit signal node 36B, and a receive signal node 36C. The common node 36A is coupled to the second input/output node 30C of the diplexer 20. The transmit signal node 36B is coupled to an output of the second power amplifier 24B. While not shown, the receive signal node 36C is often coupled to an LNA for amplifying RF receive signals provided thereto for further processing. The second duplexer 22B is configured to pass second RF transmit signals TX2 from the second power amplifier 24B between the transmit signal node 36B and the common node 36A while attenuating other signals in this path. Further, the second duplexer 22B is configured to pass second RF receive signals RX2 from the common node 36A to the receive signal node 36C while attenuating other signals in this path. Accordingly, the second duplexer 22B allows for simultaneous transmission and reception of signals in the second RF frequency band.
The first power amplifier 24A is configured to receive and amplify first modulated transmit signals MTX1 to provide the first RF transmit signals TX1. The second power amplifier 24B is configured to receive and amplify second modulated transmit signals MTX2 to provide the second RF transmit signals TX2.
The first RF coupler circuitry 26A includes a first RF coupler 38 and first attenuator circuitry 40. The first RF coupler 38 is arranged adjacent to the first RF transmission line 32A such that a portion of the RF signals provided via the first RF transmission line 32A are coupled by the first RF coupler 38 and provided to the first attenuator circuitry 40 as first RF feedback signals RF_FB1. The first attenuator circuitry 40 is coupled between the first RF coupler 38 and the feedback receiver circuitry 28 and configured to attenuate the first RF feedback signals RF_FB1 to compensate for the frequency dependence of the coupling factor of the first RF coupler 38 as well as to ensure that the first feedback signals RF_FB1 are within the dynamic range of the feedback receiver circuitry 28 over the entire power range of the signals.
The second RF coupler circuitry 26B includes a second RF coupler 42 and second attenuator circuitry 44. The second RF coupler 42 is arranged adjacent to the second RF transmission line 32B such that a portion of the RF signals provided via the second RF transmission line 32B are coupled by the second RF coupler 42 and provided to the second attenuator circuitry 44 as second RF feedback signals RF_FB2. The second attenuator circuitry 44 is coupled between the second RF coupler 42 and the feedback receiver circuitry 28 and configured to attenuate the second RF feedback signals RF_FB2 to compensate for the frequency dependence of the coupling factor of the second RF coupler 42 as well as to ensure that the second feedback signals RF_FB2 are within the dynamic range of the feedback receiver circuitry 28 over the entire power range of the signals.
The feedback receiver circuitry 28 is coupled to each one of the first power amplifier 24A and the second power amplifier 24B, such that the feedback receiver circuitry 28 is coupled between the first RF coupler circuitry 26A, the second RF coupler circuitry 26B, the first power amplifier 24A, and the second power amplifier 24B. The feedback receiver circuitry 28 is configured to receive the first RF feedback signals RF_FB1 and provide a first power amplifier control signal PA_CNT1 to the first power amplifier 24A based thereon, where the first power amplifier control signal PA_CNT1 is configured to change one or more operating parameters of the first power amplifier 24A in order to alter the transmit power of RF transmit signals provided therefrom. Further, the feedback receiver circuitry 28 is configured to receive the second RF feedback signals RF_FB2 and provide a second power amplifier control signal PA_CNT2 to the second power amplifier 24B based thereon, where the second power amplifier control signal PA_CNT2 is configured to change one or more operating parameters of the second power amplifier 24B in order to alter the transmit power of RF transmit signals provided therefrom. While not shown, the feedback receiver circuitry 28 may include one or more feedback receiver amplifiers to amplify the first RF feedback signals RF_FB1 and the second RF feedback signals RF_FB2, and signal processing circuitry for generating the first power amplifier control signal PA_CNT1 and the second power amplifier control signal PA_CNT2 based thereon. The first RF coupler circuitry 26A, the second RF coupler circuitry 26B, and the feedback receiver circuitry 28 form a closed loop feedback system in order to keep the transmit power of RF transmit signals provided from the conventional RF front end circuitry 16 within a desired range.
The conventional RF front end circuitry 16 suffers from several drawbacks. First, the conventional RF front end circuitry 16 is not suited for applications in which the diplexer 20, the first duplexer 22A, and the second duplexer 22B are replaced with a multiplexer, as is preferred in modern RF front end circuitry due to the increase in performance and decrease in area consumption associated therewith. While it is possible to create a closed loop feedback system with a multiplexer using the above approach, it would require separate RF coupler circuitry for each one of the multiplexed RF frequency bands. Such an approach would consume a large area, and thus would not be suitable for applications in which area is a design concern. Since modern wireless communications devices are supporting an ever increasing number of RF frequency bands, the conventional approach discussed above is becoming less and less desirable. In addition to the above, placing the first RF coupler circuitry 26A and the second RF coupler circuitry 26B downstream of the diplexer 20 in the conventional RF front end circuitry 16 may decrease the accuracy of measurements provided therefrom, as the diplexer 20 may cause changes in RF transmit signals as they are passed to the antenna 18. In general, it is desirable to measure the transmit power of RF transmit signals as close to the antenna 18 as possible to ensure the accuracy of these measurements. Finally, when presented with the situation identified above in FIG. 1 wherein a first RF signal with a relatively low transmit power is provided, for example, from the first power amplifier 24A and a second RF signal with a relatively high transmit power is provided, for example, from the second power amplifier 24B, the first RF signal with the relatively low transmit power is highly susceptible to intermodulation distortion due to the second RF signal with the relatively high transmit power. Accordingly, the first RF feedback signals RF_FB1 may be inaccurate, leading to undesired adjustments to the transmit power of the first RF transmit signal TX1.
In light of the above, there is a need for improved RF coupler circuitry for providing closed loop transmit power control for carrier aggregation configurations.